A lot of pharmacies offer screenings where they will perform a finger stick to test a drop of blood for you. You can also screen urine, but the blood test is more accurate.

Though, if you're not just being curious and really suspect you or someone you know is diabetic based on other symptoms, it's probably best to just schedule a doctor's appointment. They can do the screening, and at the same time, do the rest of the exam to determine the right treatment...or if it's not diabetes, to consider other things the symptoms might indicate.